return null;
    }
  }

  /** An admittedly inefficient implementation of {@link Map#containsKey}. */
  static boolean containsKeyImpl(Map<?, ?> map, @CheckForNull Object key) {
    return Iterators.contains(keyIterator(map.entrySet().iterator()), key);
  }

  /** An implementation of {@link Map#containsValue}. */
  static boolean containsValueImpl(Map<?, ?> map, @CheckForNull Object value) {

      }
    };
  }

  /**
   * Returns a "nefarious" map entry with the specified key and value, meaning an entry that is
   * suitable for testing that map entries cannot be modified via a nefarious implementation of
   * equals. This is used for testing unmodifiable collections of map entries; for example, it
   * should not be possible to access the raw (modifiable) map entry via a nefarious equals method.
   */

              : new DescendingImmutableSortedMultiset<E>(this);
    }
    return result;
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation is guaranteed to throw an {@link UnsupportedOperationException}.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @Deprecated

   * runs quickly, since the row key is provided. However, {@code column(columnKey).size()} takes
   * longer, since an iteration across all row keys occurs.
   *
   * <p>Note that this implementation is not synchronized. If multiple threads access this table
   * concurrently and one of the threads modifies the table, it must be synchronized externally.
   *

          && hashCodeInsensitiveToArgReference(
              factory, args, i, generateDummyArg(param, newFreshValueGenerator()))) {
        // If the implementation uses identityHashCode(), referential equality is
        // probably intended. So no point in using an equal-but-different factory argument.
        // We check twice to avoid confusion caused by accidental hash collision.

      super("Returned value '" + actual + "' not found. Remaining elements: " + expected);
    }

    private static final long serialVersionUID = 0;
  }

  /**
   * Quasi-implementation of {@link ListIterator} that works from a list of elements and a set of
   * features to support (from the enclosing {@link AbstractIteratorTester} instance). Instead of

  }

  /**
   * Serialized type for all ImmutableSortedMap instances. It captures the logical contents and they
   * are reconstructed using public factory methods. This ensures that the implementation types
   * remain as implementation details.
   */
  @J2ktIncompatible // serialization
  private static class SerializedForm<K, V> extends ImmutableMap.SerializedForm<K, V> {
    private final Comparator<? super K> comparator;

      }
    };
  }

  /**
   * Returns a "nefarious" map entry with the specified key and value, meaning an entry that is
   * suitable for testing that map entries cannot be modified via a nefarious implementation of
   * equals. This is used for testing unmodifiable collections of map entries; for example, it
   * should not be possible to access the raw (modifiable) map entry via a nefarious equals method.
   */

          && hashCodeInsensitiveToArgReference(
              factory, args, i, generateDummyArg(param, newFreshValueGenerator()))) {
        // If the implementation uses identityHashCode(), referential equality is
        // probably intended. So no point in using an equal-but-different factory argument.
        // We check twice to avoid confusion caused by accidental hash collision.

      return multimap.keySet();
    }

    @Override
    Iterator<K> elementIterator() {
      throw new AssertionError("should never be called");
    }
  }

  /** A skeleton implementation of {@link Multimap#entries()}. */
  abstract static class Entries<K extends @Nullable Object, V extends @Nullable Object>
      extends AbstractCollection<Map.Entry<K, V>> {
    abstract Multimap<K, V> multimap();